Top seed James Blake overcame a patchy service game to defeat South Korean qualifier Woong-Sun Jun 6-3, 7-5 and reach the quarter-finals of the Indianapolis Tennis Championships on Thursday.
Blake, ranked eighth in the world, made just 49 percent of his first serves but converted three of nine break points to defeat the 293rd-ranked Jun in 71 minutes.
Despite Blake's suspect service game, Jun was able to convert just one of eight break-point opportunities against the American, who is seeking his 11th career title.
Blake will face Lu Yen-Hsun of Taiwan, who defeated American Rajeev Ram 6-1, 7-6 in the quarter-finals.
American Bobby Reynolds, who trounced Alejandro Falla of Colombia 6-1, 6-1 also advanced and will face compatriot Sam Querrey, who defeated Vince Spadea 4-6, 6-3, 6-4.